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BRIN autosummarization may need a snapshot

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It's possible to define BRIN indexes on functions that require a
snapshot to run, but the autosummarization feature introduced by commit
7526e10224 fails to provide one.  This causes autovacuum to leave a
BRIN placeholder tuple behind after a failed work-item execution, making
such indexes less efficient.  Repair by obtaining a snapshot prior to
running the task, and add a test to verify this behavior.

Author: Álvaro Herrera <alvherre@kurilemu.de>
Reported-by: Giovanni Fabris <giovanni.fabris@icon.it>
Reported-by: Arthur Nascimento <tureba@gmail.com>
Backpatch-through: 13
Discussion: https://postgr.es/m/202511031106.h4fwyuyui6fz@alvherre.pgsql
This commit is contained in:
Álvaro Herrera
2025-11-04 13:23:26 +01:00
parent c09a06918d
commit a95e3d84c0
2 changed files with 44 additions and 4 deletions
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2
src/backend/postmaster/autovacuum.c
View File

@@ -2556,7 +2556,9 @@ deleted:
workitem->avw_active = true;
LWLockRelease(AutovacuumLock);
PushActiveSnapshot(GetTransactionSnapshot());
perform_work_item(workitem);
PopActiveSnapshot();
/*
* Check for config changes before acquiring lock for further jobs.

46
src/test/modules/brin/t/01_workitems.pl
View File

@@ -24,23 +24,61 @@ $node->safe_psql(
create index brin_wi_idx on brin_wi using brin (a) with (pages_per_range=1, autosummarize=on);
'
);
# Another table with an index that requires a snapshot to run
$node->safe_psql(
'postgres',
'create table journal (d timestamp) with (fillfactor = 10);
create function packdate(d timestamp) returns text language plpgsql
as $$ begin return to_char(d, \'yyyymm\'); end; $$
returns null on null input immutable;
create index brin_packdate_idx on journal using brin (packdate(d))
with (autosummarize = on, pages_per_range = 1);
'
);
my $count = $node->safe_psql('postgres',
"select count(*) from brin_page_items(get_raw_page('brin_wi_idx', 2), 'brin_wi_idx'::regclass)"
);
is($count, '1', "initial index state is correct");
is($count, '1', "initial brin_wi_index index state is correct");
$count = $node->safe_psql('postgres',
"select count(*) from brin_page_items(get_raw_page('brin_packdate_idx', 2), 'brin_packdate_idx'::regclass)"
);
is($count, '1', "initial brin_packdate_idx index state is correct");
$node->safe_psql('postgres',
'insert into brin_wi select * from generate_series(1, 100)');
$node->safe_psql('postgres',
"insert into journal select * from generate_series(timestamp '1976-08-01', '1976-10-28', '1 day')"
);
# Give a little time for autovacuum to react. This matches the naptime
# configured above.
sleep(1);
$node->poll_query_until(
'postgres',
"select count(*) > 1 from brin_page_items(get_raw_page('brin_wi_idx', 2), 'brin_wi_idx'::regclass)",
't');
$count = $node->safe_psql('postgres',
"select count(*) > 1 from brin_page_items(get_raw_page('brin_wi_idx', 2), 'brin_wi_idx'::regclass)"
$count = $node->safe_psql(
'postgres',
"select count(*) from brin_page_items(get_raw_page('brin_wi_idx', 2), 'brin_wi_idx'::regclass)
where not placeholder;"
);
is($count, 't', "index got summarized");
cmp_ok($count, '>', '1', "$count brin_wi_idx ranges got summarized");
$node->poll_query_until(
'postgres',
"select count(*) > 1 from brin_page_items(get_raw_page('brin_packdate_idx', 2), 'brin_packdate_idx'::regclass)",
't');
$count = $node->safe_psql(
'postgres',
"select count(*) from brin_page_items(get_raw_page('brin_packdate_idx', 2), 'brin_packdate_idx'::regclass)
where not placeholder;"
);
cmp_ok($count, '>', '1', "$count brin_packdate_idx ranges got summarized");
$node->stop;
done_testing();